The objective of this proposal is to acquire an analytical flow cytometry which will be shared by investigators at the Center for Blood Research (CBR) to conduct established and new research projects focused on various aspects of blood research. The current projects that will specifically utilize this instrument are: 1) a three-component program project focused on blood cell signaling pathways and cytoskeletal organization (Dr. Fred S. Rosen), (2) studies of the genetic and cellular mechanisms of immunity and host defense (Dr. Chester A. Alper), (3) studies of T lymphocyte function in HIV infection disease, the Wiskott- Aldrich syndrome (Dr. Eileen Remold-O-Donnell). Analytical flow cytometry us a central technical approach for all of this projects, which are funded by NIH-peer received grants, and will be used in a variety of cell and molecular biological model systems to investigate the function of blood cell surface and intracellular proteins. The results derived from these ongoing investigations will lead to a better understanding of the molecular mechanisms involved in immunity, host defense and cell differentiation and will provide fundamental information on the mechanisms that control key immunological and hematological functions. The requested Coulter Model XL flow cytometry analyzer system will enhance the productivity of these established and expanding research projects. This instrument is state-of-the-art and has features that meet the growing applications by blood research scientists to studies of the structure and function of blood cells by versatile and refined flow cytometry techniques. This instrument is capable of analyzing up to four differently labeled fluorescent probes in a single sample which increases the accuracy and decreases the cost, time and sample size required for analysis. The IBM compatible acquisition and analysis computer programs will allow both automated, high throughput analyses and specialized, refined advanced applications such as are required for kinetic measurements and quantitations of intracellular antigens.